test(no_unused_results): Add roundtrip for Test message (#1364)

Author: caspermeijn

tests/src/no_unused_results.rs

@@ -1,7 +1,14 @@
+use crate::check_message;
+
 mod should_compile_successfully {
     #![deny(unused_results)]
     include!(concat!(env!("OUT_DIR"), "/no_unused_results.rs"));
 }
 
 #[test]
-fn dummy() {}
+fn roundtrip() {
+    let msg = should_compile_successfully::Test {
+        dummy_field: "dummy".into(),
+    };
+    check_message(&msg);
+}